1. Field of the Invention
The present invention relates to a filter element that is capable of collecting carbon dusts effectively and is useful as an air cleaner, etc. of a car, an internal combustion engine, etc.
2. Description of the Prior Art
In the power source of the car, the motor bicycle, etc., the clean air is supplied to the engine by collecting the dusts by virtue of the filter element of the air cleaner in the suction system of the engine.
In recent years, the filtering function of adsorbing and filtering the dusts, a particle size distribution of which extends over a wide range from the dust with a large particle size such as a cloud of sand to the dust with a small particle size such as the carbon particle contained in the exhaust gas from the diesel car, etc. (referred to as the xe2x80x9ccarbon dustxe2x80x9d hereinafter), is required of the filter element. Also, performances such as excellent dust holding capacity (long filtering lifetime), small pressure loss, etc. are required of the filter element while maintaining a high cleaning efficiency.
In order to satisfy these requirements, the wet type filter that is formed of the filter paper or nonwoven fabric impregnated with the viscous oil and has a ridge-like-folded structure, for example, is employed. Also, the dry type filter that is formed of the filter paper, nonwoven fabric, or the like, which does not contain the oil, is employed.
As the dry type filter, in Patent Application Unexamined Publication (KOKAI) Hei. 10-85539, the filter element consisting of the main filter, which is formed of the ridge-like-folded nonwoven fabric, and the pre-filter, which is arranged on the upstream side of this main filter and formed of the nonwoven fabric, are disclosed. This filter element can improve the dust holding capacity by increasing the bulk of the pre-filter. However, the filter element cannot sufficiently increase the dust holding capacity although the expensive nonwoven fabric is used. Therefore, such filter element is disadvantageous to industrial use from the respect of cost-effectiveness. In addition, if it is tried to implement the excellent dust cleaning efficiency by the dry type filter, the bulk of the filter is increased even after the improved structure such as the ridge-like-folded structure, etc. to increase the adsorption area is employed, and thus it is difficult to get the compact filter element.
In contrast, in the wet type filter, since the viscous oil on the surface of the filter can catch the dusts, the dust absorbing amount per volume of the filter can be increased, and thus reduction in size of the filter can be attained. Also, the clogging due to the dust is hard to occur and also the high cleaning efficiency can be attained. In addition, the wet type filter has such a feature that the lifetime of the wet type filter is longer than the dry type filter. However, in the wet type filter, it is known that the carbon dusts, which are caught by the oil in the filter, get out of the filter, and thus the carbon dust cannot be effectively collected.
Therefore, it is an object of the present invention to provide a filter element having improved characteristic as being compared with the conventional filter element. In particularly, it is an object of the present invention to provide a filter element that has a high dust cleaning efficiency and a high dust holding capacity and also has a long filtering lifetime.
It is another object of the present invention to provide a filter element that is capable of improving a carbon dust cleaning efficiency, and also has a small pressure loss and a low cost.
In order to attain the above subjects, as the result of earnest studies, the inventors of the present invention have found that, if a filtering member that is not impregnated with an oil and a filtering member that is impregnated with an oil are formed in specific order, the filter element whose dust (particularly, carbon dust) cleaning efficiency can be improved, whose dust holding capacity can be enhanced, and whose filtering lifetime can be extended long can be implemented at a low cost, and have completed the present invention.
More particularly, a filter element of the present invention comprises a first filtering member, and a second filtering member that is arranged on a downstream side of the first filtering member and is impregnated with the oil, wherein the first filtering member consists of a downstream wet layer that is impregnated with the oil, which is transferred by contact to the second filtering member, and an upstream dry layer that is not impregnated with the oil.
In the above filter element, the dry layer of the first filtering member, which is not impregnated with the oil, collects mainly the carbon dust, and the wet layer, which is impregnated with the oil, adsorbs the dusts that passed through the dry layer and have a relatively large particle size, and also the second filtering member adsorbs the dusts that passed through the first filtering member. Therefore, the dust holding capacity of the overall filter can be extremely increased.
In such filter element, the oil that exists on the side at which the second filtering member comes into contact with the first filtering member is transferred to the first filtering member. As a result, the concentration gradient of the oil occurs in the overall filtering members. Thus, the presence of the oil is effective to collect the dust. However, if the oil is present excessively, lumps of the dust are formed at oil-excessive portions to cause the clogging. In contrast, if the concentration gradient that is reduced gradually from the downstream side to the upstream side is formed, such concentration gradient is effective to prevent the clogging.
A density of the first filtering member may be set smaller than a density of a filtering member constituting the second filtering member. If the density of the first filtering member is relatively smaller than the second filtering member, the clogging due to the dust can be delayed. The density of the first filtering member may be set uniformly as a whole, or may be reduced continuously or stepwise from the upstream side to the downstream side. For example, if the first filtering member has a tissue whose density is changed from a dense density to a coarse density from the upstream side (air intake side), the carbon dust can be caught and held effectively at the high-density area on the upstream side. The second filtering member may be shaped into an appropriate shape, e.g., a ridge-like-folded structure, or the like. Filtering members constituting the first filtering member and the second filtering member are formed of at least one of a filter paper and a nonwoven fabric respectively. For example, the filtering member constituting the first filtering member is formed of the nonwoven fabric, and the filtering member constituting the second filtering member is formed of the filter paper. It is possible to collect effectively the carbon dust if the first filtering member is formed of at least one of the filter paper and the nonwoven fabric, while the excellent dust adsorbing/holding capabilities can be achieved as the wet type filter if the second filtering member is formed of at least one of the filter paper and the nonwoven fabric, which are impregnated with the oil.